M. Goul'Kov et al., Threshold of oscillation in a ring-loop phase conjugator as a second-orderoptical phase transition, APP PHYS B, 72(2), 2001, pp. 187-190
The threshold behavior is studied for a ring-loop coherent oscillator with
a photorefractive strontium barium niobate (SBN) sample. A soft onset of os
cillation is revealed and critical slowing down is observed in the temporal
development of light-induced scattering below the threshold, thus pointing
to a similarity with a second-order phase transition.